The present invention relates to a method of producing an insulating element as well as to an insulating element produced according to the method.
Such insulating elements are preferably employed in the automobile industry and are used, for example, between the hot catalytic converter and the vehicle floor.
Such insulating elements are known and are described, for example, in PCT-application WO91/10560 or U.S. Pat. No. 5,424,139. WO91/10560 describes a heat shield with a foil packet which has heat conveying zones, so-called heat-sinks, and comprises heat insulating zones. In particular, the individual foils of the foil packet have embossments or knobs which result in the stacked foils being spaced from each other. The individual foils can be hermetically closely connected with each other, thus permitting the enclosure of a gas, for example xenon. In a further development of this known heat shield, and for improving its acoustical efficacy, the individual foils are perforated. In practice, the edge regions of these foil stacks are compacted without the application of any substantial pressure, cut and subsequently beaded, heat-sealed or mechanically bonded.
In U.S. Pat. No. 5,424,139 an insulating element is described which comprises a stack of several thin metal sheets, between which sheets a metallic web or a stretched metal spacer is inserted.
It has been shown that the acoustical efficacy of these foil stacks depends largely upon the perforations, the choice of material and the spacing between the individual foil sheets. In order to be able to select/predetermine these parameters, suitable foilsxe2x80x94preferably aluminium foilsxe2x80x94are guided over spiked rollers and/or knobbed rollers. If the expert wishes to alter either the knob form or knob density, the perforation density or the size of the individual perforations, extensive alterations to the tools must first be undertaken.
It is therefore a task of the present invention to provide a method for producing a sound absorbing insulating element, and in particular for producing a sound absorbing heat shield, whereby only a few processing steps are involved and adjustments or changes to the foil parameters can easily be made. In particular it is the aim of this method to allow for easy and inexpensive adjustments to be made to the perforation density and to the air-flow resistance created by such perforations.
This task is solved by a method of producing a sound-absorbing insulating element, having at least two metallic sheets in the form of foils or metal sheets, of which at least one is embossed, and said sheets being joined and formed together, wherein at least one fissured sheet is produced when, during embossing, the material of the at least one metallic sheet is overstretched to such an extent that fissures are created, and in particular by a method for producing a sound absorbing insulating part having at least two metal sheets which can be in the form of foils or thin metal lamellae. In one process step of the method, the material of at least one metal sheet is knobbed, and in a further process step this knobbed sheet is connected with at least a second metal sheet. During the knobbing or embossing of the at least one metal sheet the limit of elasticity of the sheet material is exceeded to such an extent that hairline cracks or fissures are created. With this inventive method it is possible to fissure thin metal just as well as thick foils, or leaves in the form of stretched metal sheets can be used. Furthermore, it is particularly advantageous to use aluminum as material for these leaves or sheets.
A particularly advantageous embodiment of the inventive method provides for cold-soldering the individual metal layers, in particular foils or leaves, to each other. In the following, the concept of xe2x80x9ccold-solderingxe2x80x9d is used to mean a metallurgical connection which is created by a plastic deformation of two or more neighboring/adjacent foils or leaves, during which metallurgical connection the metal of adjacent leaves undergoes a material connection. If the metal is aluminium, such a metallurgical connection is achieved when adjacent leaves are compressed by, for example, 75%.
Furthermore it is a task of the present invention to provide an insulating element, in particular a heat shield, having an improved and easily optimizable acoustical efficacy.
This task is solved by a sound absorbing insulating element, in particular a sound-absorbing heat shield, wherein the heat shield comprises at least two metallic sheets in the form of foils of metal sheets of which at least one comprises a plurality of knobs and fissures and which sheets are joined together, and in particular by a sound absorbing heat shield comprising at least two metal sheets, whereby the at least one metal sheet comprises a plurality of knobs and/or fissures and is connected to the at least second sheet and is shaped into a formed insulating element. It is particularly advantageous if these metal sheets are made of aluminum.
The inventive method has proven to be surprisingly easy to employ and leads to sound absorbing insulating elements having a surprisingly good sound absorption.